This invention relates generally to a top vacuum corrugation feeder for an electrophotographic printing machine, and more particularly, to a top vacuum corrugation feeder having movable side guides that can be adjusted for feeding a wide variety of document or copy sheet sizes.
Present high speed xerographic copy reproduction machines produce copies at a rate in excess of several thousand copies per hour, therefore, the need for a sheet feeder to feed cut copy sheets to the machine in a rapid, dependable manner has been recognized to enable full utilization of the reproduction machine's potential copy output. In particular, for many purely duplicating operations, it is desired to feed cut copy sheets at very high speeds where multiple copies are made of an original placed on the copying platen. In addition, for many high speed copying operations, a document handler to feed documents from a stack to a copy platen of the machine in a rapid dependable manner also been reorganized to enable full utilization of the machine's potential copy output. These sheet feeders must operate flawlessly to virtually eliminate the risk of damaging the sheets and generate minimum machine shutdowns due to uncorrectable misfeeds or sheet multifeeds. It is in the initial separation of the individual sheets from the sheet stack where the greatest number of problems occur.
One of the sheet feeders best known for high speed operation is the top vacuum corrugation feeder with front air knife. In this system, a vacuum plenum with a plurality of friction belts arranged to run over the vacuum plenum is placed at the top of a stack of sheets in a supply tray. At the front of the stack, an air knife is used to inject air into the stack to separate the top sheet from the remainder of the stack. In operation, air is injected by the air knife toward the stack to separate the top sheet, the vacuum pulls the separated sheet up and acquires it. Following acquisition, the belt transport drives the sheet forward off the stack of sheets. In this configuration, separation of the next sheet cannot take place until the top sheet has cleared the stack. In this type of feeding system every operation takes place in succession or serially, and therefore, the feeding of subsequent sheets cannot be started until the feeding of the previous sheet has been completed. In addition, in this type of system the air knife may cause the second sheet to vibrate independent of the rest of the stack in a manner referred to as "flutter". When the second sheet is in this situation, if it touches the top sheet, it may tend to creep forwardly slightly with the top sheet. The air knife then may drive the second sheet against the first sheet causing a shingle or double feeding of sheets. Also, some current top and bottom vacuum corrugation feeders utilize a valved vacuum feedhead, e.g., U.S. Pat. Nos. 4,269,406 and 4,451,028. At the appropriate time during the feed cycle the valve is actuated, establishing a flow and hence a negative pressure field over the stack top or bottom if a bottom vacuum corrugation feeder is employed. This field causes the movement of the top sheet(s) to the vacuum feedhead where the sheet is then transported to the take-away rolls. Once the sheet feed edge is under control of the take-away rolls, the vacuum is shut off. The trail edge of this sheet exiting the feedhead area is the criteria for again activating the vacuum valve for the next feeding. A top vacuum corrugation feeder with a valveless vacuum system is shown in U.S. Pat. No. 4,699,369 and all of the heretofore mentioned patents are included herein by reference.
Current customer requirements for middle volume machines include the furnishing of sheet feeders that handle sheets ranging in size from A6 to 12".times.18". If the port area of a vacuum feedhead of a top vacuum corrugation feeder is designed for the A6 size sheets, there may be insufficient flow and pressure to acquire and feed the larger sheets. However, if the air system is designed for the larger sheets, smaller sheets will not cover all of the port openings, allowing air leakage and reducing feeder performance. Therefore, an improved feeder is needed that will reliably feed a wide variety of sheet sizes.